ABSTRACT
OBJECTIVES: The symptoms of attention-deficit/hyperactivity disorder (ADHD) can be treated with methylphenidate, a potent blocker of the dopamine transporter (DAT). The homozygosity of the 10-repeat allele at dopamine transporter gene (DAT1) seems to be associated with a poor response to methylphenidate (MPH) in children with ADHD. In present study, we investigated association between DAT density using I-123N-(3-iodopropen-2-yl)-2beta-carbomethoxy-3beta-(4-chlorophenyl)tropane ([123I]IPT SPECT) and the homozygosity for 10-repeat allele at DAT1, and response to MPH in children with ADHD. METHODS: Eleven drug-naive children with ADHD were included in the study and treated with MPH for about 8 weeks. After the genotyping and SPECT were performed, we compared DAT density between ADHD children with and without the homozygosity for the 10-repeat allele at DAT1 and investigated correlation between the homozygosity for the 10-repeat allele and response to MPH. RESULTS: ADHD children with 10/10 genotype (n=7) had a significantly higher DAT density in basal ganglia than the children without 10/10 genotype (n=4)(Right: z=-2.65, p=0.008; Left: z=-2.65, p=0.008). We found that while only 28.6% (2/7) of the subject with 10/10 genotype showed good response (> or =50% improvement) to MPH treatment, 100% (4/4) of the subjects without 10/10 genotype showed good response to MPH treatment (chi2 test: F=5.238, df=1, p=0.022). CONCLUSION: Our findings support an association between homozygosity for the 10-repeat allele at DAT1 and the DAT density assessed in vivo and correlation between the homozygosity for the 10-repeat allele and poor response to MPH.